By aid of gas chromatography and gas chromatography-mass spectrometer，light hydrocarbons，chain alkanes，polycyclic aromatic hydrocarbons，biomarkers such as steranes and terpanes，and diamondoids in crude oils from the Kela 2 structure and Yaha structural belts in the Kuqa Depression were analyzed. The results show that various aromatic hydrocarbons are abnormally abundant in C6-8 light hydrocarbons and whole oils;C19-26tricyclic terpanes in m/z 191 mass chromatogram,and pregnane,homopregnane in m/z 217 mass chromatogram are relatively high in crude oils from the Kela 2 structure,but these biomarkers in similar crude oils from the Yaha structural belts are obviously low,suggesting that crude oils from the Kela 2 structure may have an unusual genetic mechanism. Moreover,alkyl adamantanes and alkyl diamantanes are detected in crude oils from the Kela 2 structure and Yaha structural belts,but alkyl trimantanes are only present in condensates from the Kela 2 structure,and the concentrations of various diamondoids in condensates from the Kela 2 structure are more an order of magnitude than those in crude oils from the Yaha structural belts,showing that maturity of condensates from the Kela 2 structure is much more than those of crude oils from the Yaha structural belts. Based on the relationship between MAI,MDI and RO values,RO values are about 1.9% in condensates from the Kela 2 structure,and their cracking extent may be more than 97%,showing that those condensates are typical cracking oils;RO values are about 1.2%-1.4% in crude oils from the Yaha structural belts,cracking extent of crude oils from different structure units varies from 20% to 80%,depending on filling extent of high-mature oils and gas in late period.
How to effectively identify between kerogen pyrolysis gas and oil cracked gas is always a puzzle in the genetic study of natural gas from marine strata.The hydrocarbon generation and expulsion experiments of different types of kerogen and oil were carried out in a semi-closed and semi-opened system.The simulating products were analyzed and typical cracked gases of kerogen and oil were compared.It indicates that hydrocarbon components and carbon isotope compositions of kerogen and oil cracked gas show similar characteristics,namely Ln(C2/C3)changing rules occur approximately horizontal in early thermal evolution and vertical in late evolution.In the high-over thermal evolution stage, Ln(C2/C3) values andδ13C2-δ13C3 values show rapid enlargement.This denotes the high thermal cracking process of source rocks,which is not an identifying sign about kerogen pyrolysis gas and oil cracked gas.The hydrocarbon composition and isotope compositions of natural gas are effective indicators to identify cracked gas in high thermal evolution,but are not a direct distinguishing index between kerogen pyrolysis gas and oil cracked gas.The evolutionary characteristics of non-hydrocarbon of kerogen pyrolysis gas and oil cracked gas indicate obvious difference,namely high nitrogen are predominant in kerogen pyrolysis gas and high hydrogen sulfide always occurs in oil cracked gas.So nitrogen and hydrogen sulfide abundance combed with hydrocarbon gas isotope composition can be important indicators to distinguish between kerogen pyrolysis gas and oil cracked gas.The above cognitions are coincided with geological reality of the gas field in Sichuan Basin and Tarim Basin.The synthesized analysis on hydrocarbons and non-hydrocarbons of natural gas obtains a new method to effectively distinguish kerogen pyrolysis gas from oil cracked gas.
We study the research status of thermal simulation experiment and put forward three issues worthy of attention and five important development directions.Classification according to thermal simulation system is the most widely used classification scheme. Different thermal simulation experimental systems have their own characteristics,and a suitable thermal simulation experiment system can be selected according to different experimental purposes.The closed experimental system is more suitable for the thermal simulation experiment of humic source rocks. The online analysis of open system has unique advantages in the study of volatile components. The semi open system is the most close to the thermal simulation system of the thermal evolution of the source rocks in the actual geological condition. Three key issues concerning the thermal simulation experiment are presented. The first is influence of water on the thermal simulation experiment. The second is whether convincing isotope reversal can be presented expect Fischer-Tropsch synthesis. The third is that,in the study of thermal simulation experiment,the model of hydrocarbon generation must be built in combination with the actual geological background. Five key development directions concerning the thermal simulation experiment are proposed. The first is thermal simulation experimental study on relatively low temperature and long time with water participation. The second is experimental research on thermal simulation of unconventional petroleum. The third is study on the development of pore microcracks in source rocks and the correlation of the interaction of fluid discharge in thermal simulation experiments. The fourth is experimental study on thermal simulation of carbonate source rock. The fifth is experimental study of thermal simulation related to abnormal pressure.
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